Studies on the vestibular system from several laboratories have been done on a variety of preparations using different anesthetic agents. The results of these experiments make cross comparisons difficult because of contradictory data. The proposed study is intended to determine the effect of group of drugs on identified vestibular cells. The application of drugs will be both systemically via the intravenous route and microiontophoretically. Experiments will be done on cats made decerebrate at the precollicular level. The initial surgery will be done under ether anesthesia but ether will be discontinued at least three hours before recordings are taken. Stimulating electrodes will be placed on branches of the VIIIth nerve to each semicircular canal. Bipolar electrodes for recording the stimulating will be placed in the ascending or descending medial longitudinal fasciculus (MLF) or the lateral vestibulospinal tract. Single cell recordings will be made from identified second order vestibular neurons and their response to intravenous or iontophoretic administration of drugs studied. The drugs to be investigated include the cholinergic system drugs, acetylcholine, physostigmine, atropine, and nicotine, and diazepam.